1. Field of the Invention
The present invention relates to an acceleration/deceleration method for controlling one movable object driven by one axis to pursue another movable object driven by another axis in an industrial machine such as a wrapping machine and a machine tool.
2. Description of the Related Art
In a generally adopted conventional acceleration/deceleration method, a follower axis (which drives a movable object to pursue another movable object driven by an objective axis) is accelerated/decelerated so that only a velocity of the follower axis is made equal to a velocity of the objective axis. For example, in a case of controlling the velocity Vx of the follower axis X to pursue the velocity Vy of the objective axis Y with a velocity difference Ve therebetween, as shown in FIG. 1, a motion of the follower axis X is delayed by an amount in the case where an acceleration/deceleration control (a linear acceleration/deceleration control in this example) is performed as indicated by the continuous line in comparison with the case where no acceleration/deceleration control is performed as indicated by the broken line to produce a positional displacement between the follower axis X and the objective axis Y. In the case where the objective axis moves at an initial velocity Vy and the following axis X moves at an initial velocity Vx0 when a pursuing command is issued (t=0), the velocity Vx of the follower axis X reaches the target velocity Vy of the objective axis Y at a time te by the linear acceleration/deceleration control. Assuming that an initial positional displacement is xe2x80x9c0xe2x80x9d at the starting of the pursuing motion, a positional displacement corresponding to an area S1 (=Vexc3x97te/2) remains after and the velocity Vx of the follower axis X equals the velocity Vy of the objective axis Y to make the velocity difference Ve xe2x80x9c0xe2x80x9d.
As described, according to the conventional acceleration/deceleration method, the position of the follower axis X is displaced with respect to the position of the objective axis Y to cause a positional displacement between the positions of the two axes although the velocity Vx of the follower axis X is made coincide with the velocity Vy of the objective axis Y. In general, it is preferable to make the position as well as the velocity of the follower axis coincides with the position and the velocity of the objective axis Y, respectively in controlling the follower axis X in synchronism with the objective axis Y.
An object of the present invention is to provide an acceleration/deceleration method capable of controlling a follower axis to pursue an objective axis so that a velocity and also a position of the follower axis coincide with a velocity and a position of the objective axis, respectively.
According to an aspect of the present invention, the acceleration/deceleration method comprises the steps of: obtaining a positional difference between positions of an objective axis and a follower axis and a velocity difference between velocities of the objective axis and the follower axis; performing a predetermined acceleration/deceleration processing based on the positional difference and the velocity difference, so that the position and the velocity of the follower axis coincide with the position and the velocity of the objective axis, respectively.
According to another aspect of the present invention, the acceleration/deceleration method comprises the steps of: obtaining a sum of a positional displacement between the follower axis and the objective axis from a start of an acceleration/deceleration, and an initial positional difference between the follower axis and the objective axis at the start of the acceleration/deceleration; and controlling a time period of the acceleration and a time period of the deceleration of the follower axis so that the sum of the positional displacement and the initial positional difference is made zero when the velocity of the follower axis coincides with the velocity of the objective axis.
Conditions of an initial positional difference and an initial velocity difference between the objective axis and the follower axis may be sorted into a plurality of cases and the velocity of the follower axis may be obtained for each case. Further, the positional difference and the velocity difference between the follower axis and the objective axis may be used as dynamic conditions for obtaining the velocity of the follower axis in the acceleration/deceleration, and the acceleration/deceleration may be dynamically performed by determining velocity of the follower axis based on the dynamic condition.
Different acceleration/deceleration values may be set for the acceleration of the follower axis with respect to the objective axis and for the deceleration of the follower axis with respect to the objective axis. Further, the velocity of the follower axis may be limited not to exceed a predetermined value.
According to still another aspect of the present invention, the acceleration/deceleration method comprises the steps of: obtaining a positional difference between the positions of the objective axis and the follower axis and a velocity difference between the velocities of the objective axis and the follower axis; setting acceleration/deceleration values for acceleration and deceleration of the follower axis; and starting acceleration/deceleration of the follower axis in response to an acceleration/deceleration start command, and controlling the follower axis so that the velocity of the follower axis pursues to coincide with the velocity of the objective axis through an acceleration process and a deceleration process with the set acceleration/deceleration value. A change-over from the acceleration process to the deceleration process or from the deceleration process to the acceleration process of the follower axis is determined based on the positional difference between the objective axis and the follower axis and a motion amount of the follower axis with respect to a motion amount of the objective axis from time of the change-over of the acceleration/deceleration to time when the velocity of the follower axis reaches the velocity of the objective axis.
A constant velocity process where the follower axis is driven at a constant velocity may be interposed between the acceleration process and the deceleration process.